This invention relates to component lubrication and/or cooling, in a reciprocatory, piston-in-cylinder device and is particularly concerned with lubrication of a piston, connecting rod and associated small-end joint and bearing assembly for an internal combustion engine.
The provision of separate fluids for dedicated lubrication and cooling is well-known. There also is typically some overlap, duality, or cooperative interaction, between lubrication and coolant roles. Some lubricants, such as oil, provide lower surface contact friction and transport heat between components differentiated by a temperature gradient.
Heat transfer to the lubricant/coolant is generally initially by conduction and convection, whereupon the lubricant/coolant is moved bodily to a cooler station, perhaps even a dedicated heat exchanger, such as an oil cooler radiator matrix, to give up its heat, allowing for return of cooler lubricant/coolant. For a heat or thermodynamic cycle engine, in the conversion of combustion heat energy into useful mechanical work output, considerable heat wastage arises, which must be disposed of, otherwise excessive local temperatures and attendant thermal stresses may lead to material and component failure.
A piston is a critical internal combustion (IC) engine component, in direct contact with intense combustion heat. Piston lubrication and cooling is particularly critical for heavy-duty operation, such as with high b.m.e.p., two-stroke, compression-ignition (diesel) engines. Special (hollow) piston configurations, with internal coolant galleries and pathways, have been proposed to address this. See, for example, pending UK application No. 9909034.2 which relates to certain piston coolant gallery refinements.
Aspects of the present invention are applicable to both air cooled and water cooled engines; to both spark-ignition (petrol, gasoline or gas) and compression-ignition (diesel) combustion modes and fuels; and to both two-stroke and four stroke combustion cycles.
Typically, in the majority of spherically-jointed, piston-connecting rod assemblies in IC engines, lubricant (oil) for joint and piston cooling is passed through crankshaft passages, or oil-ways, and along a passage, or oil-way, in the connecting rod itself, and collected in a central cavity in a (hollow) piston body, around the connecting rod small end.
Aspects of the present invention address the provision of lubricant (oil) to a spherical small end joint and attendant piston cooling. It is to be understood, however, that the present invention is broadly applicable to other small end joint configurations, such as those envisaged in the Applicants co-pending UK patent application no. 9908844.5 on piston retention.
According to one aspect of the invention, a (hollow) piston, has a localized lubricant (oil) and/or coolant reservoir, configured as a (central) piston cavity, with one or more passages or grooves, in a (part)spherical, {or (part-)cylindrical} under-crown surface, communicating, though one or more passages, pathways, or oil-ways, with an integrated coolant gallery. In practice, such passages or grooves in the piston under-crown ensure that the upper portion of the small end joint is provided with a supply of xe2x80x9cfreshxe2x80x9d (i. e. cooler) lubricant, under pressure, whilst carrying lubricant to the integral piston coolant gallery. Provision of a plentiful lubricant supply reduces the wear rate and the risk of scuffing and galling, and carries away any wear debris.
Various groove (cross-sectional) profiles, contours, positions and layouts may be employed consistent with preservation of simple or practical (i.e. not overly convolute) lubricant (oil) flows and manufacturing simplicity, economy, quality and consistency. Thus, for example, (part) spiral, or helical, forms could be employed.
Relatively small diameter passages, pathways, or oil-ways, can be adoptedxe2x80x94in the feed and/or return pathsxe2x80x94in order to optimize lubricant (oil) flow into the piston gallery. In practice, some form of (flow) restriction may be desirable, otherwise the capacity of a lubricant (oil) pump in an engine (re-)circulatory lubricant system would have to be enlarged considerably in order to maintain an adequate lubricant (oil) supply pressure to the bearings. Such flow restriction could be an orifice or passages connected over some part only of each engine cycle.
The piston could be cast in aluminum alloy with a steel connecting rod, although other suitable materials could be used.